Abstract : As part of a projected long-term study of the role of virus-specific cellular immune responses in the outcome of togavirus infections, the present experiments have explored: (1) the basis for the differing patterns of morbidity and mortality produced in various inbred strains of mice intracerebrally infected with the neuro-adapted AR339 strain of Sindbis virus (SV) and, (2) attempted to demonstrate whether such infections induce SV-specific cytotoxic T lymphocyte responses and how such responses might correlate with resistance or susceptibility to SV. It was found that infections of mice having a BALB/c background usually are self-limiting and non-fatal whereas mice with C3H or C57BL backgrounds exhibit high mortality. Based on mortality patterns of SV-infected H-2 congenic and H-2 recombinant mice, no association could be made between resistance/susceptibility and genes mapping to the K, I or D regions of the major histocompatibility (H-2) complex. Thus far, evidence for SV-specific cytotoxic T lymphocyte responses has not been obtained in either resistant or susceptible mouse strains suggesting that this type of immune effector mechanism may not be important in recovery from alphavirus infections. (Author)